'Sloop of war' definitions:

Definition of 'sloop of war'

noun

A sailing or steam warship having cannons on only one deck

From: GCIDE

Sloop \Sloop\, n.[D. sloep, of uncertain origin. Cf. Shallop.]
1. (Naut.) A vessel having one mast and fore-and-aft rig, consisting of a boom-and-gaff mainsail, jibs, staysail, and gaff topsail. The typical sloop has a fixed bowsprit, topmast, and standing rigging, while those of a cutter are capable of being readily shifted. The sloop usually carries a centerboard, and depends for stability upon breadth of beam rather than depth of keel. The two types have rapidly approximated since 1880. One radical distinction is that a sloop may carry a centerboard. See Cutter, and Illustration in Appendix. [1913 Webster]
2. (Naut.) In modern usage, a sailing vessel having one mast, commonly with a Bermuda rig, with either a center-board or a keel. In the United States, a sloop may have one or two headsails, while in Western Europe and Great Britain a sloop has only one headsail. [RDH]
Sloop of war, formerly, a vessel of war rigged either as a ship, brig, or schooner, and mounting from ten to thirty-two guns; now, any war vessel larger than a gunboat, and carrying guns on one deck only. [1913 Webster]

From: GCIDE

Corvet \Cor"vet\ (k?r"v?t), Corvette \Cor*vette"\ (k?r-v?r"), n. [F. corvette, fr. Pg. corveta or Sp. corbeta, fr. L. corbita a slow-sailing ship of burden, fr, corbis basket. Cf. Corbeil.] (Naut.) A war vessel, ranking next below a frigate, and having usually only one tier of guns; -- called in the United States navy a sloop of war. [1913 Webster]